Graves' disease is an autoimmune disorder in which 40-60% of patients develop Graves' ophthalmopathy, also called Thyroid Eye Disease (TED). TED is characterized by expansion of the orbital fat compartment and extraocular muscles (Prabhakar et al., Endocr Rev 24(6):802-835 (2003)). Intense inflammation and infiltration of immune cells, including T cells, macrophages and mast cells, in the retrobulbar space of TED patients are key factors that drive the proliferation and differentiation of orbital fibroblasts to adipocytes (Lehmann et al., PPAR Res, Art. ID. 895901 (2008); Feldon et al., Am J Pathol 169(4):1183-1193 (2006)). In addition to the adipogenic potential of orbital fibroblasts, these cells are also key producers of extracellular matrix glycosaminoglycans (GAG). One of the key pathological findings in TED patients is the over-production and accumulation of the GAG hyaluronan (HA). The extremely hydrophilic nature of HA leads to remarkable increases in tissue volume and to the anterior displacement of the eye, or exophthalmos (Smith et al., J Clin Endocrinol Metab 89(10):5076-5080 (2004)), resulting in the disfigurement and vision impairment (Kuriyan et al., Curr Opin Ophthalmol 19(6):499-506 (2008)) characteristic of TED.
HA is synthesized as an acidic, negatively charged, high molecular weight polysaccharide via the actions of hyaluronan synthases (HAS) (Jiang et al., Annu Rev Cell Dev Biol 23:435-461 (2007)), of which there are three isoforms: HAS1, HAS2 and HAS3. Increased HA synthesis closely correlates with the expression levels of HAS (Makkonen et al., J Biol Chem 284(27):18270-18281 (2009)), which are themselves induced by growth factors, cytokines (Makkonen et al., J Biol Chem 284(27):18270-18281 (2009); Campo et al., Br J Biomed Sci 66(1):28-36 (2009); Guo et al., J Biol Chem 282(17):12475-12483 (2007)) and prostaglandins (PG) (Honda et al., “Prostaglandin E2 Stimulates Cyclic AMP-mediated Hyaluronan Synthesis in Rabbit Pericardial Mesothelioma Cells,” Biochem J. 292:497-505 (1993); Fischer et al., Thromb Haemost 98(2)287-295 (2007)). One PG that may have an important implication in TED is PGD2. PGD2 is a metabolite of arachidonic acid that is formed by the actions of cyclooxygenases (Cox) and PGD2 synthases (PGDS) (Goetzl et al., Faseb J 9(11):1051-1058 (1995); Herlong et al., Immunol Lett 102(2):121-131 (2006)). Many of the biological actions of PGD2 are mediated through two G protein-coupled receptors, DP receptor 1 (DP1) and DP2 (also called chemoattractant receptor-homologous molecule (CRTH2)) (Boie et al., J Biol Chem 270(32):18910-18916 (1995); Nagata et al., FEBS Lett 459(2):195-199 (1999); Kostenis et al., Trends Mol Med 12(4):148-158 (2006)). These receptors elicit divergent effects by the coupling to either Gs (DP1) or Gi (DP2) to elevate cyclic AMP (cAMP) or intracellular calcium (Ca2+), respectively. PGD2 can also spontaneously undergo a series of dehydration reactions to form the PGJ family of prostaglandins, including 15d-PGJ2, an endogenous ligand for the peroxisome proliferator-activated receptor (PPARγ) (Forman et al., Cell 83(5):803-812 (1995); Kliewer et al., Cell 83(5):813-819 (1995)).
Human orbital fibroblasts express PPARγ and PPARγ is crucial for the differentiation of fibroblasts to adipocytes. A recent publication reported that activated human T lymphocytes isolated from patients with TED produce much more PGD2-derived PGs compared to T cells from healthy individuals (Feldon et al., Am J Pathol 169(4):1183-1193 (2006)). Mast cells are also a key cellular source of PGs, with PGD2 being the major prostanoid released (Feldon et al., Am J Pathol 169(4):1183-1193 (2006); Lewis et al., J Immunol 129(4):1627-1631 (1982)). Mast cells are a central immune cell in the pathogenesis of TED. Not only is there intense mast cell infiltration and degranulation (Lauer et al., Ophthal Plast Reconstr Surg 24(4):257-261 (2008)) associated with adipocytes (Boschi et al., Br J Ophthalmol 89(6):724-729 (2005)) in TED patients, but co-culture of mast cells with orbital fibroblasts up-regulates HA synthesis (Smith et al., Endocrinology 140(8):3518-3525 (1999)). It remains unknown whether this increase in HA production by orbital fibroblasts is the result of PGD2 acting via the direct modulation of DP receptors or via some other means. Further, it would be desirable to identify therapies for TED that can reliably decrease HA production within the retro-ocular space.
The present invention is directed to overcoming these and other limitations in the art.